The successful outcome of RSA depends greatly on proper soft tissue tension. Since the rotator cuff is either absent or severely compromised and irreparable, the stability of the shoulder joint comes from significant deltoid tension holding the ball and socket joint together.
Existing reverse shoulder systems require a surgeon to pick a trial liner and reduce the shoulder joint with that liner assembled into a humeral cup. If the correct liner is chosen, the soft tissue tension is significant, requiring the surgeon to apply extreme force to the humerus and surrounding soft tissues to reduce the joint. If no additional damage is done during this reduction process, the joint must then be dislocated to allow the surgeon to implant a joint replacement prosthesis.
Dislocation can often be more difficult than reduction and RSA patients often have compromised bone stock and/or soft tissue. The extreme force required to dislocate the joint again may put the patient at risk for other injury and soft tissue trauma. Furthermore, current systems require the surgeon to use a trial and error approach in establishing proper soft tissue tension. This often takes several attempts before adequate stability is achieved.
There currently exists a need for an adjustable trial including an insert that rotatably engages a humeral cup. The insert may first be inserted into the humeral cup and then rotated into a fully collapsed or neutral position. Such a device may allow a surgeon to easily reduce the shoulder joint. Preferably, the insert may then be advanced to a position where optimal deltoid tension is achieved. At this position, the insert and humeral cup are preferably calibrated such that the surgeon may determine a liner thickness corresponding to a dialed position of the insert with respect to the humeral cup. The terms “dialed position” or “dial in” indicate the distance between a proximal end of the insert and a proximal end of the humeral cup. This distance or liner thickness is measured by indications on the insert, such as calibration marks and/or attachment locations in reference to a marker on the humeral cup. This will be further explained in the detailed description.
The surgeon may also perform range of motion (“ROM”) and joint stability analyses during calibration of the trial. Preferably, the surgeon may then easily collapse the trial back to the neutral position and simply dislocate the joint. Further, the trial may also be preferably expanded prior to joint reduction and collapsed prior to joint dislocation repeatedly, depending on surgeon preference. Once the trial has been optimized, a surgeon preferably records the dialed position of the expanded trial. This measurement should preferably be the liner thickness. If this measurement does not correspond to the size of a particular liner in the system, the surgeon may select a next larger sized liner. At this time, the surgeon may remove the trial and then implant a prosthesis including a humeral cup and the selected liner.